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September 2013

Thursday, 08/15/13 | 5087 reads

How-To Insights On Orthotic Modifications For Patients With Diabetes

For a plantar ulcer on the second metatarsal head, Dr. Kirby suggests modifying the orthosis to accommodate the second metatarsal head in the forefoot extension area of the orthosis, which will place greater pressures on the first, third, fourth and fifth metatarsal heads. In addition, he says one may also modify the orthosis to have a metatarsal pad proximal to the second metatarsal head to increase the plantar pressure on the distal second metatarsal shaft and off the second metatarsal head.

Dr. Kirby says another possible modification would be adding a bar forefoot post or "dropoff" across all the metatarsal necks to increase the plantar pressures across all the distal metatarsal shafts. This should reduce the plantar pressures across all the metatarsal heads, according to Dr. Kirby.

Dr. Kirby says the sum total of ground reaction force acting on the plantar foot does not decrease with foot orthoses. However, he notes foot orthoses do have the potential to effectively redistribute ground reaction force to different areas of the plantar foot and hopefully away from the high pressure at-risk areas of the plantar skin.

“Once the biomechanics of plantar pressure reduction is understood, then the only limitation to foot orthosis therapy for patients with diabetes is the imagination and skills of the prescribing podiatrist,” says Dr. Kirby.

Can Orthotics Prevent Re-Ulceration In Patients With Diabetes?

By Brian McCurdy, Senior Editor

Patients with diabetes can be at risk for re-ulceration, making prevention a top priority. A recent study in the Journal of the American Podiatric Medical Association notes that custom orthotics can reduce plantar pressures and prevent subsequent ulcers.

The authors focused on 117 patients with a history of diabetic foot ulcers who received prescription insoles after having never before worn orthotics. After two years of wearing insoles, the re-ulceration rate decreased from 79 percent to 15 percent and the amputation rate declined from 54 percent to 6 percent.

As Kevin Kirby, DPM, notes, the literature indicates foot orthoses are very effective at not only reducing peak plantar pressures in patients with diabetes but also at facilitating the healing of existing ulcerations. He cites a study in Diabetic Medicine in which orthoses caused a 30 percent reduction in maximum peak pressure in 81 patients with type II diabetes.

As Dr. Kirby advises, the degree of neuropathy and presence of existing ulcerations or pre-ulcerations should spur concern about not only the foot orthosis design and construction but the patient’s shoes as well. He notes that in patients with significant neuropathy, softer and thicker topcovers, which can help reduce peak pressures and shearing forces, can be the difference in preventing ulcers. If the patient already has a plantar ulcer or has a high risk of ulcer recurrence, Dr. Kirby suggests that shoes may need the addition of rocker soles or sole accommodations.

There is “very little doubt” that high pressures contribute to the development of diabetic foot ulcers in people with diabetes with and without neuropathy, according to David G. Armstrong, DPM, PhD, MD, the Director of the Southern Arizona Limb Salvage Alliance in Tucson, Ariz.

“Reduced pressure should be a priority for anybody working to prevent these problems,” he says.

Dr. Armstrong concurs with Dr. Kirby about research showing the benefits of orthoses in reducing pressures. He hopes to develop a model to measure normal and shear stress before and after shoe prescription.

“The bottom line is that neuropathic patients do not have the ability to sense high pressure spots on their plantar skin either with or without foot orthoses under their feet,” notes Dr. Kirby, an Adjunct Associate Professor within the Department of Applied Biomechanics at the California School of Podiatric Medicine at Samuel Merritt University in Oakland, Calif. “The podiatrist must therefore monitor these high-risk patients accordingly with more careful, frequent orthosis follow-ups and adjustments than what they otherwise schedule for their non-neuropathic patients.”

If the goal of foot orthosis therapy for patients with diabetic neuropathy is the reduction in pressures at high pressure areas on the plantar foot, Dr. Kirby suggests designing the orthosis with a biomechanical knowledge of how to reduce plantar pressures without causing other pathologies. To reduce plantar pressures effectively with an orthosis, the orthosis must cause a reaction force in areas of the plantar foot other than existing high pressure areas. However, Dr. Kirby cautions that this redistribution of orthosis reaction force to other areas of the plantar foot must not cause pathologic magnitudes of compression or shear forces, which could potentially cause ulceration in other areas of the foot.

Study: PAD Is On The Rise Worldwide

By Danielle Chicano, Editorial Associate

Lower extremity peripheral artery disease (PAD) can lead to amputation, difficulty walking, heart attack and stroke. Now a new report shows a significant increase in the worldwide prevalence of PAD.

According to a recent review in The Lancet that looked at 34 studies, the number of people with PAD has increased worldwide from 164 million in 2000 to 202 million in 2010. The study added that among the 202 million people living with PAD in 2010, 69.7 percent of them live in low-income or middle-income countries in Southeast Asia and the Western Pacific region.

Risk factors that contribute to the instance of PAD in both high and low to middle-income countries include smoking, diabetes, hypertension and hypercholesterolemia, according to the study.

Kazu Suzuki, DPM, CWS, attributes increased medical problems including diabetes, PAD and other atherothrombotic diseases to the “graying” of America.

“I do believe we are seeing more and more patients with extremely advanced age (90 to 100 years old),” says Dr. Suzuki, the Medical Director of the Tower Wound Care Center at the Cedars-Sinai Medical Towers in Los Angeles. “It makes perfect sense that we are seeing more PAD as it is just a natural process of aging just like osteoarthritis or skin wrinkles.”

Dr. Suzuki notes that approximately one-third of his patients with diabetes have at least a mild case of PAD.

“Based on many studies, we know that this number gets much worse as the age increases beyond 65 years old and if they have comorbidities such as diabetes, end-stage renal disease or if they are smokers,” says Dr. Suzuki.

According to Dr. Suzuki, most insurance companies as well as Medicare do not reimburse screening tests for PAD. He says this precludes more frequent use of screening tools such as ankle brachial test or skin perfusion pressure tests for patients who are at high-risk for PAD “although this may change in the near future with a focus on preventative medicine.”

Dr. Suzuki notes that his wound care center generally strongly suspects that a patient has either coronary artery disease (CAD) or PAD if they are more than 65 years old. The threshold for suspicion drops to age 50 in patients who have diabetes or smoke. If a new patient presents with limb pain, claudication or rest pain, he recommends testing for PAD with a type of non-invasive Doppler test.

“Based on the test results, I would make a treatment recommendation to follow up with their primary care physician (for mild PAD) or immediate consultation with vascular specialists (for moderate to severe PAD),” adds Dr. Suzuki.

Investigators for two phase 3 studies enrolled about 600 patients each, who applied tavaborole once a day for 48 weeks, according to the manufacturer Anacor Pharmaceuticals. In the two studies, 6.5 percent and 9.1 percent of patients taking tavaborole achieved the primary endpoint of complete cure in comparison, respectively, to 0.5 percent and 1.5 percent of patients who used a vehicle agent, according to the company.

Anacor submitted a new drug application to the Food and Drug Administration (FDA) in July and the company says it expects the approval and launch of tavaborole in mid-2014.

Warren Joseph, DPM, says tavaborole is a novel class of antifungal, noting that no new topical antifungal has received FDA approval since ciclopirox (Penlac) 14 years ago. Unlike with Penlac, which required debridement every month, he notes the tavaborole studies expressly did not allow debridement but still found tavaborole to be effective. As it is a solution, tavaborole is easier to apply and it dries more quickly than the lacquer formulations, according to Dr. Joseph, a Fellow of the Infectious Diseases Society of America and a consultant to Anacor Pharmaceuticals.

Max Weisfeld, DPM, feels tavaborole has several specific advantages over ciclopirox, saying the smaller molecular weight of tavaborole allows a greater penetration of the nail plate to get to the site of the infection. In contrast, he says ciclopirox tends to accumulate on top of the nail plate. Another advantage of tavaborole, states Dr. Weisfeld, is that it is water soluble, allowing for penetration of the nail, and is active in the presence of keratin, a main component of the nail plate.

Dr. Weisfeld, a principal investigator on the phase 3 trials, also speculates that even though debridement is optional for patients using tavaborole, debridement might improve the efficacy of the antifungal. In addition, Dr. Weisfeld has found tavaborole to have little or no detectable systemic exposure.

“I think that the ‘holy grail’ of onychomycosis was always to find a safe, effective, easy to apply topical since so many people, to this day, do not want to take oral agents and risk even the minimal chance of a toxicity,” says Dr. Joseph. “I will say that with the upcoming potential approvals of both tavaborole and efinaconazole (Valeant Pharmaceuticals), there is certainly more ‘excitement’ about the topic than there has been.”

Comments

Plantar redistribution of force and shear is paramount for healing and protection.

Use of an external sole rocker or the newer technology of using a levered internal midsole shoe rocker can achieve this.

Use of compressible foams to donut hole a lesion is helpful or the newer technology of using a composite spring plate with lesion cuttouts is very helpful to not only reduce pressure but shear as well by transferring the force distally and plantar through the spring plate. Modified carbon fiber dynamic AFOs work very well for this but have only been really used for stroke support. We should start using the AFOs if we want to maximize our orthotic therapies.

Mahalo,

Dr. King

Co-Principal Investigator SBIR A11-109 "Advanced Composite Insoles for the Reduction of Stress Fractures." US Department of Defense and Army Medical Research and Materials Command,